River Markets
River Markets is a unified prime brokerage for prediction markets, consolidating multiple exchanges — Kalshi, Polymarket, and Polymarket US (with Novig and Rothera planned) — behind a single account, order-management system, and REST + WebSocket API. Every contract across all venues is assigned a unified River ID, so professional and institutional traders can search markets, place and route orders (including icebergs, pegs, stop-losses, and take-profits with smart order routing), track positions and P&L across isolated subaccounts, and stream live fills, orderbooks, orders, and trade prints from one integration. Requests are Ed25519-signed so the private key never leaves the client process. Founded by ex-BlackRock and high-frequency trading quants and backed by Y Combinator (Spring 2026).
Limited machine-readable signal and partial portal coverage — documentation a human can read, but little a machine or agent can consume without scraping.
API Evangelist profiles River Markets the way a machine reads it — 31 machine-readable artifacts across 1 API, pulled from the provider's own public surface and indexed so a developer, an analyst, or an AI agent can evaluate it against every other provider on the network.
Every provider in the network is reduced to the same set of machine-readable artifacts — OpenAPI contracts, event specifications, GraphQL schemas, runnable collections, pricing and rate-limit signals, security posture, OAuth scopes, and the agent surfaces (MCP servers and skills) that let software drive the API on its own. We profile them because the interface is the part of a company you can actually inspect: it is a truer signal of what a provider does than any marketing page. From those artifacts we compute the Kin Score — River Markets scores 35.8/100 (thin), with a separate agent-readiness read of 27/100 (agent aware). The full breakdown is below, followed by every artifact we hold — each card links through to its machine-readable definition on apis.io.
Kin Score
This is the API Evangelist rating — a single, repeatable read computed from the artifacts on this page. Green fill is points earned; the red track is points possible, so every bar shows earned-versus-possible at a glance. Every facet and dimension name is a link: it opens that measurement's page on APIs.io, where the rating runs across the whole catalog — the exact checks that feed it, how every profiled provider distributes on it, and who is at the top of it.
Kin Score
How this is scored →scored 2026-09-08 · rubric v0.20.0
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How we profile River Markets
Each block below is one kind of artifact we hold for River Markets. For each we say what it is and why it earns a place in the profile, then list every one we've indexed — capped at two rows, scroll within the panel for the rest.
APIs 13
Each API is captured as its own OpenAPI definition — every operation, parameter, and response. This is the single most useful machine-readable description of what an API does, and it's what lets us score, lint, mock, and generate against it without asking the provider for anything.
Individual APIs this provider publishes, each with its own machine-readable definition.
River Markets balance API
The balance API from River Markets — 1 operation(s) for balance.
River Markets complex-orders API
Manage complex orders: conditional orders (take-profit and stop-loss), TWAP, and other advanced order types.
River Markets fair-values API
The fair-values API from River Markets — 2 operation(s) for fair-values.
River Markets fills API
Retrieve trade execution history and fill details.
River Markets generic-assets API
The generic-assets API from River Markets — 3 operation(s) for generic-assets.
River Markets markets API
Search and discover prediction markets across Kalshi and Polymarket.
River Markets orderbooks API
The orderbooks API from River Markets — 2 operation(s) for orderbooks.
River Markets orders API
Place and manage orders on prediction market exchanges.
River Markets positions API
View current portfolio positions across all connected exchanges.
River Markets prices API
Get historical price data and candlesticks from exchanges.
River Markets subaccounts API
Manage trading subaccounts. Each subaccount can have its own exchange credentials and positions.
River Markets tradeprints API
Recent trades for a market. Pairs with the /v1/ws/tradeprints WebSocket for live updates.
River Markets watchlists API
The watchlists API from River Markets — 4 operation(s) for watchlists.
Scroll within the panel for all 13 ·
Open Collections 14
Open, tool-agnostic collections carry the same runnable value as Postman without locking you to one client — the portable, forkable form of the same exercise.
Open, tool-agnostic API collections (OpenAPI-derived and Bruno).
API Collection
OPEN COLLECTIONRiver Markets balance API
OPEN COLLECTIONRiver Markets balance complex-orders API
OPEN COLLECTIONRiver Markets balance fair-values API
OPEN COLLECTIONRiver Markets balance fills API
OPEN COLLECTIONRiver Markets balance generic-assets API
OPEN COLLECTIONRiver balance markets API
OPEN COLLECTIONRiver Markets balance orderbooks API
OPEN COLLECTIONRiver Markets balance orders API
OPEN COLLECTIONRiver Markets balance positions API
OPEN COLLECTIONRiver Markets balance prices API
OPEN COLLECTIONRiver Markets balance subaccounts API
OPEN COLLECTIONRiver Markets balance tradeprints API
OPEN COLLECTIONRiver Markets balance watchlists API
OPEN COLLECTIONScroll within the panel for all 14 ·
Event Specifications 1
Not every API is request/response. AsyncAPI describes the event-driven and streaming side — the webhooks and channels — so the asynchronous half of the interface is documented the same way the synchronous half is.
AsyncAPI definitions for this provider's event-driven and streaming APIs.
River Markets Streaming API
Real-time WebSocket streams over wss://api.rivermarkets.com. Client frames are JSON text; server frames are orjson-serialized UTF-8 bytes. Handshake auth uses the Ed25519 signed...
ASYNCAPISecurity Posture 2
Authentication, domain security, vulnerability disclosure, and trust-center signals — the evidence that a provider takes security seriously enough to document it. We profile it because you can't govern what you can't see.
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Agentic Access 1
An x-agentic-access contract marks which operations are safe for an agent to run on its own and which need a human in the loop. It is the difference between an API an agent can use and one it can use safely.
Recommended x-agentic-access execution contracts for AI agents.
Resources
Every other property we hold for River Markets — documentation, portals, status pages, policies, and corporate surface — grouped by the job it does, following the integrator's arc from getting started to running in production.
Get Started 3
Portal, sign-up, and the first successful call
Documentation 4
Reference material describing how the API behaves
Agent Surfaces 4
MCP servers, agent skills, and machine-readable catalogs
Design & Contract 5
Pagination, idempotency, versioning, errors, and events
Build 3
SDKs, sample code, and the tooling you integrate with
Access & Security 2
Authentication, authorization, and security posture
Company 1
The organization behind the API
Other 2
Properties that don't map to a standard resource type
← All providers · Data indexed from github.com/api-evangelist/river-markets · machine-readable index on apis.io
This is an independent, third-party profile of River Markets, published by API Evangelist. We do not operate, host, resell, or support these APIs, and we are not affiliated with or endorsed by the company unless stated above. Everything here is built from publicly available information — the company's own site, developer portal, documentation, public repositories, and the specifications it publishes for public use. Nothing is obtained by breaching a system, defeating an access control, or using credentials.
The Kin Score and Agent Readiness rating are independently calculated assessments of a company's public API artifacts, scored against a published rubric. They are not certifications, endorsements, security assessments, or audits.
Corrections, re-scores, and removal are free — no partnership or purchase required, and you do not need to justify the request. A removed company is recorded as unrated, never scored zero for having asked. Acknowledgement within one business day; removal within two.
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